Solar heating systems in the past have been completely filled with a collector fluid, except for a small expansion volume in the surge tank.
The present solar system departs from past practice in one aspect in that a refrigerant, such as the fluorinated hydrocarbons, is used as the collector fluid. Only the collector is filled with liquid refrigerant, the balance of the system containing refrigerant gas according to the pressure-temperature relationship of the refrigerant. Normally, there are no pressure reducing valves or pressure regulating valves used in the system. The entire system being basically under the same pressure, such control devices may be dispensed with. However, this is not to exclude the use of such structures under certain conditions. The pressure will be determined by the condensing temperature in the heat dissipator.
In past practice, sensible heat of the collector fluid is raised in the collector as heat is picked up. The collector fluid is then circulated by a pump (using some energy) to a heat exchanger or heat dissipating or storage device.
In the present invention, latent heat of the refrigerant is picked up causing the liquid refrigerant to "boil" and change to vapor according to the amount of heat picked up. Vapor pressure immediately travels to the heat dissipating device where it condenses and returns as a liquid to the collector, this being a continuous procedure as long as heat is being absorbed by the collector.
Now, since latent heat is being used for heat movement instead of sensible heat, if the load at the heat dissipator is equal to the heat input at the collector, the pressure in the system will remain constant and not increase. Therefore, the collector plate temperature can remain lower than in old style systems where sensible heat is picked up. Since the Delta T in the collector is greater, the efficiency of a collector can be much greater than for old style collector fluid charged systems.
Also, the response to sudden bursts of sunlight is almost instantaneous in a refrigerant charged system and it will be picking up and transferring usable heat before the old style collector fluid charged system can get started.
Whenever the heat dissipator is located above the collector, a circulating pump can usually be eliminated. When desired to locate the heat dissipator below or near the same height as heat pick up, a small refrigerant circulating pump is used. However, since latent heat of the refrigerant is used instead of sensible heat, a relatively small weight of refrigerant needs to be circulated and very little power is required.
A refrigerant charged system is very useful in picking up an abundance of "low-grade" heat for use in heat pumps. Heat may be transferred from the ground or storage tanks or phase change materials for use in heat pumps with the expenditure of very little or no energy.
Obviously, this system may be used for picking up heat and moving it inside to a radiator, or fan coil, or heat dissipating plate, or water heater, or heat exchanger primary, or for storage in water, masonry, phase change materials and the like.
The present invention comprises a component for such a system which will control flow of refrigerant in the system to allow flow only as such times when the temperature, and consequently the pressure, of the refrigerant is low enough so that the system may be operated safely. The component is located in the liquid refrigerant return line between the heat dissipating structure and the collector structure. A thermostatically controlled valve is provided in the component. This valve closes at a predetermined temperature causing a stoppage of flow of liquid refrigerant back to the collector structure from the heat dissipating structure. This results in all refrigerant being condensed into the heat dissipating structure whereupon the system becomes inoperative. Therefore, the maximum system temperature is regulated without external means or controls or external wiring.
The component provides additional structure including a convenient valve evaluating, charging and servicing for the system and provides a connection for a permanent pressure gauge if desired. The component is useful in installing, servicing, checking as to the amount of charge and controlling the maximum system temperature and pressure.